MLA

McNally, Rand, and Company. Wyoming Highway Map, 1955 / Wyoming State Highway Commission ; Prepared by Rand McNally & Co. Wyoming State Highway Commission? :, Wyoming Tourist Bureau?, 1955. https://collections.library.yale.edu/catalog/15818402.

APA, 6th edition

McNally, R., & C. (1955). Wyoming highway map, 1955 / Wyoming State Highway Commission ; prepared by Rand McNally & Co. [Road maps]. Wyoming State Highway Commission? :, Wyoming Tourist Bureau?, https://collections.library.yale.edu/catalog/15818402.